People continue to demand better and better quality for low-power color liquid crystal displays. In some special applications, for example for large-screen LCOS (Liquid Crystal On Silicon) projection displays, the requirements include photo-realistic images, fast and accurate colors, and high light efficiency. So far, no color light switch exists that can accept strong light illumination and absorb close to zero light in the process.
Currently, two major technologies dominate the use of liquid crystal displays for displaying color. The most common is STN-LCD and TFT-LCD, which use color filters to determine its basic colors that cannot be changed by external means. Another is Electrically Controlled Birefringence (ECB) liquid crystal display technology, where the basic colors are obtained by controlling the voltages applied to the liquid crystal layer to change the retardation. The light mostly concentrates in the center, thus it is not as clear around the edges, and light efficiency is low. Neither of these technologies can change colors quickly. Also, both technologies use polarizers and color filters that absorb light. When strong light is shone on the imagers used for projection displays, the temperature will rise to a point where it exceeds the normal operating range of the imager. Thus, color displays based on current liquid crystal technologies cannot fulfill the needs of color projection.